While fetching the custom fields details added using ACF, you need to use the functions from the plugin.
Use the_field to echo the value and get_field to retrieve the value.
Here you can use
<p><?php echo get_field( 'show_this_tomorrow', $prev_post->ID ); ?></p>
or
<p><?php the_field( 'show_this_tomorrow', $prev_post->ID ); ?></p>